Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 721: Following are larval control measures, except:

A. DDT (Correct Answer)
B. Gambusia
C. Intermittent irrigation
D. Paris green

Explanation: ***DDT*** - **DDT (dichlorodiphenyltrichloroethane)** is primarily classified as an **adulticide** in vector control programs, used mainly for **indoor residual spraying** to kill adult mosquitoes. - While DDT can kill larvae when applied to water, it is **not typically categorized as a larval control measure** in public health practice due to environmental concerns and its primary use against adult vectors. - Its mechanism involves interfering with the **nervous system** of insects, causing paralysis and death. *Paris green* - **Paris green** is a chemical compound historically used as a **larvicide**, particularly effective against **Anopheles larvae** in stagnant water. - It works as a **stomach poison** for larvae when ingested during feeding, making it a specific larval control agent. *Gambusia* - **Gambusia**, also known as **mosquitofish**, are small fish that feed on mosquito larvae, making them a **biological control measure** for larval populations. - They are often introduced into ponds, ditches, and other water bodies to naturally reduce larval numbers. *Intermittent irrigation* - **Intermittent irrigation** is an **environmental manipulation method** that involves draining and refilling water sources at regular intervals, effectively destroying **larval breeding sites**. - This method prevents larvae from completing their development cycle by eliminating the aquatic environment they depend on.

Question 722: Which of the following diseases is specifically under surveillance by the World Health Organization for mandatory notification by national health authorities under the International Health Regulations (IHR) 2005?

A. Relapsing fever
B. Paralytic polio (Correct Answer)
C. Louse-borne typhus fever
D. All of the options

Explanation: ***Paralytic polio*** - **Poliomyelitis due to wild-type poliovirus** is one of only three diseases requiring **mandatory notification** under **Annex 2 of the International Health Regulations (IHR) 2005**, regardless of context or scale. - The other two diseases requiring mandatory notification are **smallpox** and **human influenza caused by a new subtype** (SARS was added subsequently). - This reflects the global commitment to **polio eradication** under the **Global Polio Eradication Initiative (GPEI)**. - Rapid detection and reporting of wild poliovirus cases trigger immediate public health responses, including **vaccination campaigns**, **surveillance intensification**, and **outbreak response activities**. *Relapsing fever* - While a serious infectious disease caused by *Borrelia* species, relapsing fever is **not specifically designated** for mandatory notification under IHR 2005. - Surveillance is typically managed at **national or regional levels** based on local epidemiological priorities and disease burden. - May require notification to WHO if it meets criteria for potential PHEIC through the decision algorithm. *Louse-borne typhus fever* - Caused by *Rickettsia prowazekii*, louse-borne typhus is a significant public health concern but is **not among the diseases requiring mandatory notification** to WHO under IHR 2005. - Surveillance efforts are guided by **local disease burden**, outbreak potential, and epidemic risk. - Like relapsing fever, would require notification only if meeting PHEIC criteria. *All of the options* - This option is incorrect because only **paralytic polio** (specifically wild-type poliovirus) is listed for **mandatory notification** under IHR 2005 among the given choices. - IHR 2005 focuses on a **select group of diseases** with potential for international spread and severe public health impact, not all infectious diseases.

Question 723: In the context of AIDS control programs, which sexually transmitted infection is specifically treated with the blue-colored pack?

A. Urethral discharge
B. Scrotal swelling
C. Genital ulcers (Correct Answer)
D. Ano-rectal discharge

Explanation: ***Genital ulcers*** - The "blue-colored pack" in AIDS control programs is specifically designed for the syndromic management of **genital ulcer disease (GUD)**. - Treating GUD is crucial for AIDS control strategies because genital ulcers facilitate **HIV transmission** by breaking the mucosal barrier. *Urethral discharge* - Urethral discharge is typically managed with the **green-colored pack**, which targets pathogens commonly causing urethritis. - This symptom primarily indicates **gonorrhea** or **chlamydia**, which are distinct from genital ulcers in their syndromic management. *Scrotal swelling* - Scrotal swelling is managed with the **white-colored pack**, which focuses on conditions like **epididymitis** or **orchitis**. - This syndromic approach addresses infections causing inflammation of the testes and epididymis, which are different from GUD. *Ano-rectal discharge* - Ano-rectal discharge is generally addressed with the **green-colored pack**, similar to urethral discharge, targeting pathogens like **gonorrhea** and **chlamydia**. - While anogenital infections can manifest in various ways, discharge from the anorectal area is managed differently from genital ulcers.

Question 724: Which of the following countries has never reported any indigenous cases of rabies?

A. New Zealand (Correct Answer)
B. United Kingdom
C. Japan
D. Iceland

Explanation: ***New Zealand*** - **New Zealand** has strict **biosecurity measures** and is one of the few countries globally to have **never recorded any indigenous case of rabies**, making it a **rabies-free country**. - The absence of rabies is maintained through rigorous **quarantine regulations** for imported animals and a lack of indigenous host species for the virus. *United Kingdom* - The **United Kingdom** has experienced sporadic cases of **rabies**, primarily in **bats** (bat lyssavirus), although it has been officially declared free from **terrestrial rabies** since 1992. - Imported cases in animals or humans have occurred, making it distinct from countries that have never had any rabies cases. *Japan* - **Japan** successfully **eliminated rabies** in 1957 through extensive vaccination programs and strict animal control measures. - While it is currently considered **rabies-free**, Japan **had endemic rabies historically** before elimination, unlike New Zealand which never had the disease. *Iceland* - **Iceland** is also considered **rabies-free** with no recorded indigenous cases, similar to New Zealand, largely due to its **geographic isolation** and **strict animal import regulations**. - However, **New Zealand** is the most commonly cited example of a rabies-free nation in medical literature due to its size and comprehensive biosecurity program.

Question 725: Which of the following statements about the DOTS treatment for tuberculosis is correct?

A. Case finding 80%, cure rate 85%
B. Case finding 80%, cure rate 80%
C. Case finding 70%, cure rate 75%
D. Case finding 70%, cure rate 85% (Correct Answer)

Explanation: ***Case finding 70%, cure rate 85%*** - The **DOTS strategy** set a global target of detecting at least **70% of new sputum smear-positive TB cases** and curing at least **85% of these cases**. - Achieving these targets was considered crucial for controlling the spread of **tuberculosis** at a population level. *Case finding 80%, cure rate 85%* - While a **cure rate of 85%** is a key target of the DOTS strategy, the **case finding target was not 80%**. - Setting a higher case finding target might be desirable, but the **established goal** for DOTS was slightly lower to be more achievable. *Case finding 80%, cure rate 80%* - Neither the **case finding target nor the cure rate target** for DOTS was 80%. - The **cure rate target** was specifically emphasized as being higher to ensure effective treatment outcomes and prevent drug resistance. *Case finding 70%, cure rate 75%* - While **case finding 70%** aligns with the DOTS target, the **cure rate target was higher than 75%**. - A lower cure rate would indicate less effective treatment management, potentially leading to **treatment failures** and the emergence of **multidrug-resistant TB**.

Question 726: Which of the following statements about Kyasanur Forest Disease is false?

A. Transmitted by bite of infective ticks
B. Incubation period of 3 to 8 days
C. Caused by Flavivirus
D. Man to man transmission is seen (Correct Answer)

Explanation: ***Man to man transmission is seen*** - Kyasanur Forest Disease is primarily an **enzootic cycle** involving monkeys, rodents, and ticks; there is **no evidence of direct person-to-person transmission**. - While humans can become infected, they are considered **dead-end hosts** and do not typically transmit the virus to other humans. *Caused by Flavivirus* - **Kyasanur Forest Disease virus (KFDV)** is indeed an **RNA virus** belonging to the genus Flavivirus and the family Flaviviridae. - This classification is accurate and important for understanding its biological characteristics. *Transmitted by bite of infective ticks* - The primary vector for KFDV transmission to humans and animals is the **hard tick, Haemaphysalis spinigera**, which becomes infected after feeding on infected monkeys or other small mammals. - **Tick bites** are the main mode of transmission; direct contact with infected animals can also lead to infection. *Incubation period of 3 to 8 days* - The typical incubation period for Kyasanur Forest Disease in humans is indeed **3 to 8 days** after exposure to the virus, though it can range from 3 to 10 days. - This relatively short incubation period leads to rapid onset of symptoms once infected.

Question 727: The incubation period of staphylococcal food poisoning is:

A. 4-6 hours (Correct Answer)
B. 6-12 hours
C. 12-18 hours
D. 18-24 hours

Explanation: ***4-6 hours*** - Staphylococcal food poisoning is caused by **preformed enterotoxins** produced by *Staphylococcus aureus* in contaminated food. - The incubation period typically ranges from **1-6 hours**, with most cases presenting within **2-4 hours** of ingestion. - The rapid onset of symptoms is due to the direct action of these **toxins** on the gastrointestinal tract, rather than bacterial multiplication within the host. - Among the given options, **4-6 hours** represents the upper range of this short incubation period. *6-12 hours* - An incubation period of 6-12 hours is more characteristic of foodborne illnesses caused by bacteria that need to **colonize** and **multiply** in the intestine, such as **Clostridium perfringens**. - *Staphylococcus aureus* food poisoning involves preformed toxins, which leads to a much **shorter incubation period**. *12-18 hours* - This incubation period is typically seen in foodborne illnesses caused by organisms like **Salmonella species** or **Campylobacter jejuni**. - These pathogens require a longer time to **colonize** and produce their effects in the host. *18-24 hours* - An incubation period of 18-24 hours or longer is common for foodborne illnesses like **Shigellosis** or certain **viral gastroenteritides**. - These conditions involve **bacterial invasion** or **viral replication**, which takes more time to manifest symptoms.

Question 728: Iceberg phenomenon is not seen in:

A. AIDS
B. Polio
C. Measles (Correct Answer)
D. Rubella

Explanation: ***Measles*** - The **iceberg phenomenon** describes a situation where only a small proportion of a disease's cases are clinically apparent (the "tip of the iceberg"), while many more cases are subclinical or undiagnosed (the "submerged base"). - Measles is characterized by a **high attack rate** and **classic clinical presentation** in almost all infected individuals, meaning nearly every infection leads to identifiable symptoms and is thus visible "above the waterline." *AIDS* - AIDS (Acquired Immunodeficiency Syndrome) is a classic example of the iceberg phenomenon, where the clinically apparent cases (AIDS diagnoses) represent a small fraction of the total infections with **HIV (Human Immunodeficiency Virus)**. - Many individuals with HIV infection are **asymptomatic for years** before progressing to AIDS, remaining undiagnosed and representing the submerged portion of the iceberg. *Polio* - Polio (Poliomyelitis) is another well-known example where the iceberg phenomenon is observed. - For every paralytic case of polio, there are **hundreds of asymptomatic or abortive cases** that are not clinically recognized, forming the large, submerged base of the iceberg. *Rubella* - Rubella (German Measles) also exhibits the iceberg phenomenon, especially concerning its impact during pregnancy. - Many rubella infections are **asymptomatic or very mild**, leading to a significant number of cases going undiagnosed, particularly in adults, yet they can still result in severe consequences like **Congenital Rubella Syndrome** if acquired during pregnancy.

Question 729: Which of the following is not caused by Aedes aegypti?

A. Japanese encephalitis (Correct Answer)
B. Yellow fever
C. Dengue
D. Filaria

Explanation: ***Japanese encephalitis*** - **Japanese encephalitis virus** is transmitted primarily by mosquitoes of the genus *Culex*, particularly ***Culex tritaeniorhynchus*** - ***Aedes aegypti* does NOT transmit Japanese encephalitis** - this is the key distinguishing feature - *Culex* mosquitoes breed in rice paddies and other stagnant water bodies, maintaining the transmission cycle between pigs, birds, and humans *Yellow fever* - *Aedes aegypti* is the primary vector for yellow fever virus in urban transmission cycles - Also transmits yellow fever in sylvatic (jungle) cycles in endemic areas of Africa and South America *Dengue* - *Aedes aegypti* is the principal vector for all four serotypes of dengue virus worldwide - Highly adapted to urban environments, breeding in artificial water containers - Responsible for the global dengue pandemic affecting tropical and subtropical regions *Filaria* - While *Aedes aegypti* is not a major vector for lymphatic filariasis, it can occasionally be involved in transmission in certain regions - The primary vectors for filariasis are ***Culex quinquefasciatus*** (urban areas), *Anopheles* species (rural areas), and *Mansonia* species - *Wuchereria bancrofti* and *Brugia malayi* are the main filarial parasites causing lymphatic filariasis

Question 730: The incubation period of diphtheria is:

A. 14-15 days
B. 2-3 days (Correct Answer)
C. 5-7 days
D. 21 days

Explanation: ***2-3 days*** - The typical **incubation period** for diphtheria, caused by *Corynebacterium diphtheriae*, is **2-5 days**, with an average of 2-4 days. - **2-3 days** falls well within this established range and represents the most common timeframe from exposure to symptom onset. - This period allows for bacterial multiplication in the upper respiratory tract and initial toxin production by toxigenic strains. *5-7 days* - While diphtheria can occasionally have an incubation period extending to 5-7 days, this represents the **upper limit** of the typical range (which is generally cited as 2-5 days). - Most cases manifest symptoms within 2-4 days, making 5-7 days less characteristic of the usual presentation. - According to standard references like **Park's Textbook of Preventive and Social Medicine**, the incubation period is 2-5 days, making 5-7 days slightly beyond the typical range. *14-15 days* - An incubation period of **14-15 days** is significantly longer than what is observed for diphtheria. - Such a prolonged period would make contact tracing and outbreak control more difficult and doesn't align with the known epidemiology of diphtheria. - This duration would be more characteristic of diseases like pertussis or certain viral infections. *21 days* - An incubation period of **21 days** is far too long for diphtheria. - Diphtheria symptoms develop relatively rapidly due to the potent and fast-acting diphtheria toxin produced by *Corynebacterium diphtheriae*. - Such a long incubation would be more typical of diseases like measles (10-14 days), chickenpox (10-21 days), or certain other infections with slower progression.

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